The medullary ascending limb is impermeable to water. Sodium (Na), potassium (K) and chloride (Cl) ions are reabsorbed by active transport. K is passively transported along its concentration gradient through a K leak channel in the apical aspect of the cells, back into the lumen of the ascending limb. This K ``leak'' generates a positive electrochemical potential difference in the lumen. This drives more paracellular reabsorption of Na, as well as other cations such as magnesium (Mg) and importantly calcium Ca due to charge repulsion.

OPTIONS:
- no
- yes

is the thick ascending limb permeable to water?

A: no


Few airlines fly between cities having a great circle route over Antarctica. Nonstop flights between South Africa and New Zealand, or between Perth, Australia and certain destinations in South America (including Buenos Aires and São Paulo), would overfly Antarctica, but no airline has scheduled such flights. Flights between Australia and South America and between Australia and South Africa pass near the Antarctic coastline. Depending on the winds, the Qantas flight QF 63 from Sydney to Johannesburg-O.R. Tambo sometimes flies over the Antarctic Circle to latitude 71 degrees as well and allowing views of the icecap. Qantas also flies nonstop between Sydney and Santiago de Chile, the most southerly polar route. Depending on winds, this flight may reach 55 degrees south latitude, but other times 71 degrees, which is enough to cross the polar ice cap. The polar route across the remote southern Pacific Ocean between South America and Oceania was pioneered by Aerolineas Argentinas, which began service between Buenos Aires via Rio Gallegos to Auckland in the 1980s with a Boeing 747-200 aircraft. Aerolineas Argentinas later operated to Sydney, but ended its flights to New Zealand and Australia in 2014.

OPTIONS:
- no
- yes

can you fly directly over the south pole?

A: no


Glucose syrup containing over 90% glucose is used in industrial fermentation, but syrups used in confectionery contain varying amounts of glucose, maltose and higher oligosaccharides, depending on the grade, and can typically contain 10% to 43% glucose. Glucose syrup is used in foods to sweeten, soften texture and add volume. By converting some of the glucose in corn syrup into fructose (using an enzymatic process), a sweeter product, high fructose corn syrup can be produced.

OPTIONS:
- no
- yes

is glucose syrup the same as high fructose corn syrup?

A: no


Sodium channels are integral membrane proteins that form ion channels, conducting sodium ions (Na) through a cell's plasma membrane. They are classified according to the trigger that opens the channel for such ions, i.e. either a voltage-change (``Voltage-gated'', ``voltage-sensitive'', or ``voltage-dependent'' sodium channel also called ``VGSCs'' or ``Nav channel'') or a binding of a substance (a ligand) to the channel (ligand-gated sodium channels).

OPTIONS:
- no
- yes

are voltage-gated sodium channels always open?

A:
no